Conventionally, frequency regulation (FR) technique which regulates power system frequency by means of a storage battery has been known. In the FR technique, it is desired to charge and discharge the storage battery while keeping the charge level of the storage battery within a predetermined allowable range.
Patent Literature (PTL) 1 intends to keep the charge level of a storage battery within an allowable range, and discloses a control technique for keeping the charge level of the storage battery within an allowable range by correcting a control variable to be provided to the storage battery when the charge level of the storage battery has deviated from the allowable range.